1. Field of the Invention
The present invention relates to the measurement of the relative weight proportions of different size fractions of a sample of particulate material.
2. Description of the Prior Art
Measurement of the size of particles in a particulate mass is required in a great many industrial operations. Much of this particle sizing is now accomplished manually by having a technician expose samples of the powder to a series of sieves -- pans with woven wire bottoms -- from which, by weighing the amounts passing and retained, he can calculate percentages of particles having certain sizes. Numerous difficulties are encountered, however with sieving as now practiced. Sieves, especially the finer meshs, are fragile. If misused, their openings are likely to be distorted, greatly biasing subsequent results obtained with them. Sieve openings very readily become blocked with irregularly shaped particles of near opening size, if too much force is exerted in trying to cause them to pass. Then the sieve has to be cleaned carefully, or again its openings will be disturbed. The weight of powder passing and retained must separately be obtained which leads to the possibility of errors in recording weights or manipulating the powder fractions. Also, the operator must determine when all the powder that can pass a sieve has done so. This, being often a judgement decision, leads to non-reproducibility. Finally, dry sieving is frequently utilized simply because it eliminates the drying of fractions even though wet sieving gives better particle dispersion, and hence, more representative results.
My previous patent describes a method and apparatus for determining the relative weight proportions of different size fractions of the sample of particulate material. However, my previously described apparatus is manually operated creating a need for an improved method and apparatus for fractionating a sample of particulate material into discrete size fractions.